The invention concerns a measuring cable travel sensor.
Measuring cable travel sensors are travel or distance-measuring sensors operating on the principle of a measuring cable, with a housing which is suitable for use in industrial situations. A typical travel sensor of that kind comprises a precisely defined and positioned cable drum on to which a measuring cable is wound, generally only in a single layer on the drum. One end of the measuring cable is suitably fixed to the cable drum. The other free end of the measuring cable is secured to the body or article, the variation in the position of which is to be precisely measured.
When the movable body or article moves away from or towards the cable drum of the measuring cable travel sensor, the resulting angular movements of the measuring cable drum about its axis are converted into a precise travel or distance length by means of a rotary angle sensor which is non-rotatably coupled to the cable drum. A rotary torsion spring which is operatively connected to the cable drum, generally in coaxial relationship therewith, ensures that the measuring cable is wound on to the cable drum when the movable body whose position is to be measured moves towards the cable drum, thereby to ensure that the measuring cable is properly wound on to the drum and is kept in a reasonably taut condition.
It will be noted that measuring cable travel sensors of such a kind are used in the most widely varying technical situations and assemblies, for example for determining the position of an elevator cabin in an elevator shaft, for continuously monitoring the angular positions of ailerons, control elevators and vertical rudders in aircraft and the like.
In order to achieve the desired level of measurement accuracy for such a measuring cable travel sensor, it is necessary on the one hand to ensure absolute angular truth as between the measuring cable drum and the rotary angle sensor. That inter alia requires free unimpeded rotary movement of the cable drum of the measuring cable travel sensor, under all operating conditions, as any impediment to the rotation of the cable drum could grossly falsify the measurement result. Accordingly on the one hand the cable drum must be reliably and dependably supported to permit it to rotate freely and accurately while on the other hand there is no way in which the measuring cable drum could be permitted to have its rotary movement adversely affected for example by the cable drum rubbing or the like against the housing or another component as a consequence of a mechanical loading, thermally induced distortion or the like of one of the components of the assembly.
For that reason the housings for measuring cable travel sensors were hitherto composed of a plurality of stable metal parts, more specifically on the one hand tube portions and on the other hand end plates which were respectively screwed together in the appropriate configuration.
The production of injection-molded parts of plastic material or die-cast parts of light metal or alloy has been less wide-spread both for reasons of the number of items involved and also because of the inadequate degree of accuracy, in comparison with the use of end plates and tube portions which are produced by a procedure which involves cutting machining.
In order to provide an arrangement in which the cable drum is reliably supported and free to rotate, the cable drum has hitherto generally been non-rotatably arranged on a separate shaft which is supported in the housing of the measuring cable travel sensor, and that shaft on which the cable drum is disposed is non-rotatably connected to a trunnion portion of the shaft of the rotary position sensor not directly but by way of a coupling which can compensate for angular displacement. In that case, the rotary angle sensor itself was generally fixed on the outside of the housing so that only the projecting trunnion portion of the sensor shaft extends into the housing.
Such designs of measuring cable travel sensors are cost-intensive because of the metal parts for the housing, which are expensive to machine, and they are also relatively large in the axial direction because of the separate support arrangement for the cable drum and the consequentially necessary angle coupling transmission to the rotary angle sensor.
An object of the present invention is to provide a measuring cable travel sensor which can be of a compact structural size, more especially in its axial direction, and which is simple and inexpensive to produce.
Another object of the present invention is to provide a measuring cable travel sensor which will afford accurate and reliable measurement results while nonetheless being of a simple design configuration.
Still another object of the present invention is to provide a measuring cable travel sensor which is of a robust structure such as to be capable of withstanding severe operating conditions.
Yet another object of the present invention is to provide a measuring cable travel sensor which affords the possibility of adaptation to different dimensional aspects in consideration of the operational situations in which it is to be employed.
In accordance with the principles of the present invention the foregoing and other objects are attained by a measuring cable travel sensor comprising a housing in which a measuring cable drum and a rotary spring are disposed. A rotary angle sensor is connected to the housing. The sensor has a shaft including a trunnion portion which projects out of the sensor. The cable drum is non-rotatably fixed in concentrically aligned relationship on the trunnion portion of the sensor shaft, in the axial longitudinal region of the trunnion portion where it projects from the sensor.
As will be appreciated from a description hereinafter in greater detail of a preferred embodiment of the measuring cable travel sensor according to the invention, a reduction in the size thereof in the axial direction is achieved by virtue of the elimination of the coupling referred to hereinbefore in connection with the previous designs. That is made possible by the avoidance of angular displacement as between the shaft of the cable drum and the sensor shaft, insofar as the cable drum is fitted on to the trunnion portion of the sensor shaft. In that respect, the cable drum does not have to be non-rotatably fixed directly on the sensor shaft, but it is possible also to use a concentric adaptor which is disposed therebetween. That can afford the advantage that the adaptor can project in the axial direction beyond the free end of the trunnion portion of the sensor shaft and can serve as a central, for example slotted entrainment means for the rotary or torsion spring which is disposed in the housing and which is axially spaced in relation to the cable drum.
The basic point of departure in terms of all stability considerations relating to the housing is thus the location of the connection between the rotary angle sensor and the housing. In order to permit inexpensive manufacture of the housing in the form of a molded or cast component of plastic material or light metal or alloy, more especially for example aluminum or ZN-casting, with the additional weight advantage that this entails, while affording adequate stability and strength, the housing comprises first and second half-shell portions which are fitted to each other, namely a shell portion which accommodates the rotary spring and a shell portion which accommodates the sensor, both of those being of a substantially cup-shaped configuration.
While however the rotary spring shell portion has a closed bottom, the sensor shell portion has a bottom region with a sensor opening through which the trunnion portion of the sensor shaft can project into the housing. The sensor itself is fitted to and secured to the sensor shell portion on the outside thereof. In the housing, the assembly comprising the adaptor and the cable drum is non-rotatably disposed on the trunnion portion of the sensor shaft by suitable mounting means such as clamping screws.
A very simple but nonetheless very strong and stable connection between the sensor shell portion and the sensor itself is achieved in accordance with another preferred feature of the invention by arranging on the inside of the sensor shell portion a stabilising ring in the form of a plate which comprises for example metal and which is of approximately the same size as the end face of the sensor or is of a somewhat larger outside periphery.
The stabilising ring is provided with screwthreaded bores and is screwed with a plurality of screws in a distributed array around the periphery, through the bottom of the sensor shell portion, using holding clips which mount the sensor to the sensor shell portion. For that purpose at its outside periphery the substantially cylindrical sensor has radially inwardly directed openings, preferably for example in the form of a peripherally extending annular groove, into which noses of the above-mentioned holding clips engage. When the sensor has a peripherally extending annular groove therein therefore instead of individual holding clips it is possible to use two semicircular ring clips which are each screwed to the internally disposed stabilising ring by way of a plurality of screw means. That affords a strong stable connection between the sensor and the sensor shell portion of the housing, with the connection in particular involving a substantial surface area such as not to allow strong torque forces acting at points.
In addition in accordance with a preferred feature of the invention the sensor shell portion is stiffened outside the region of contact of the stabilising ring therewith, with radially outwardly rising first radial ribs which are distributed over the entire periphery of the assembly. However the radial ribs do not extend continuously radially as far as the side walls of the sensor shell portion but terminate radially inwardly to such an extent that the casing of the cable drum which is of T-shaped or L-shaped cross-section can rotate radially outwardly of those first radial ribs, wherein the casing of the cable drum axially engages behind the radial ribs. It is only outside the region of the cable drum which rotates at that location that second radial ribs then in turn extend in an inclinedly rising configuration from the bottom of the sensor shell portion to the side walls thereof.
In accordance with another feature of the invention while the sensor shell portion, as considered in cross-section, has only one single region of the same depth and of the same free diameter, the spring shell portion is of a stepped configuration in the axial direction thereof.
The region of the spring shell portion which is of smaller diameter and which is of substantial depth in the axial direction thereof accommodates the rotary spring while the axially shallower but larger-diameter region which is therefore disposed radially around the smaller-diameter region corresponds to the dimensioning of the sensor shell portion and like same must accommodate the cable drum as, when considered in the axial direction, the plane of contact between the sensor shell portion and the rotary spring shell portion is disposed either in the region of the cable drum or in the region between the cable drum and the spring, but also in the larger-diameter region of the spring shell portion in order here to afford some play and clearance to allow for different axial lengths of the cable drum to permit different cable drums to be fitted to the arrangement.
The spring shell portion is also ribbed in a radial direction, but preferably with radial ribs which remain of the same height in their radial extent, more specifically both in the region of the bottom of smaller-diameter region and also in the region of the bottom part which extends therearound externally thereof. Arranged at the transition between the two regions of the spring shell portion are mounting pins or projections which are directed towards the sensor shell portion and on to which can be fitted a stop cover which closes off the end of the receiving region for accommodating the spring so that the spring is held at both faces thereof between the bottom part of the receiving region for accommodating the spring on the one hand and the above-mentioned cover on the other hand, and thus has a contact surface for supporting it at both faces of the spring.
In order to permit the peripheral casing portion of the cable drum to engage behind the first radial ribs of the sensor shell portion, as indicated above, the cable drum is of a T-shaped or L-shaped configuration when considered in cross-section, that is to say the radial plate member of the cable drum is not arranged on the end of the cable drum that is towards the sensor shell portion, but either centrally or on the end thereof, which is remote therefrom, in relation to the peripheral casing of the cable drum.
In addition the contact plane of the housing also extends through a cable entry connection portion which more particularly is preferably formed in one piece with the respective shell portions of the housing. The cable entry portion is preferably subdivided into a plurality of chambers which adjoin each other at different radial spacings relative to the axis of the housing so that, depending on the respective diameter of the cable drum in other aspects, cable guide elements for the cable entry can be selectively disposed in one chamber of the cable entry portion or another.
In accordance with a further preferred feature of the invention the housing is of a substantially quadrangular such as rectangular configuration in its external contour, wherein the screw means between the two shell portions constituting the housing are arranged in corner regions thereof, with the cable entry portion also being disposed in a corner region. That corner region also has the screw means between the different chambers which can be put to use of the cable entry portion.
In accordance with another preferred feature the housing and thus the entire measuring cable travel sensor can be secured in relation to other units and assemblies not by means of screws passing through the housing, which could give rise to problems in terms of maintaining sealing integrity, but instead the outside surfaces of the housing preferably have fixing grooves which are more preferably arranged parallel to the axial direction of the measuring cable travel sensor so that the housing of the measuring cable travel sensor can be fixed to the component supporting it by means of holding clips which can be screwed to that component, in a position of co-operating with the above-mentioned grooves.
As the cable entry portion is in operation heavily subjected to a wear loading by virtue of the cable sliding thereagainst, the cable entry portion is preferably generally provided with a spout-shaped cable guide portion which is fitted into the wall of the desired chamber of the cable entry portion, although it can also be formed in one piece therewith. The cable guide portion is preferably made from polyether ethylene ketone (PEEK) which is particularly resistant to high temperature and abrasion wear. PEEK can also be injection-molded or produced from the solid by cutting machining.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of a preferred embodiment thereof.